Probably a "unilaterally" or similar adverb is implicit.I feel more precise language is required here, as the GM should be in charge of these elements, only basing them on the characters rather than the setting.
In my experience it's not trivial to explain the difference, because even "unilateral" is probably not quite right - as per a recent thread looking at the advice to GMs in the 3E D&D DMG, it is possible to be not completely unilateral yet still set up a railroad (the example is of having the quest-giver offer as their reward something that speaks to some player-established concern).
I'm happy to discuss further if you think it's worthwhile.